Indepth Electrical engineering

Here’s a detailed breakdown of the required tests for 66 kV and 132 kV XLPE cables per IS 7098 (Part 3) (covering 66 kV up to and including 220 kV), with reference to IS 60840 equivalents where applicable: IS 7098 (Part 3): Tests for 66 kV & 132 kV XLPE Cables Based on the BIS Product Manual for IS 7098 (Pt 3) , the following tests are specified—applicable to each completed length of cable and per manufacturing batch/consignment ( BIS ): 📋 Test Checklist for 66 kV & 132 kV XLPE Power Cables Standards Referenced: IS 7098 (Part 3), IS 60840 / IEC 60840 1. Routine Tests (Every Delivered Cable Length) Test Sequence Acceptance Criteria Conductor resistance Pre-insulation ≤ values specified in IS 7098 (as per cross-section & temp. corrected to 20 °C) Partial Discharge (PD) test After manufacturing, before HV PD ≤ 5 pC at 1.5 × U₀ (U₀ = pha...

It has been often found that most of think that material used for earthing will reduce earthing resistance. It has been often misconception that copper earthing plate or rod will have lower earth pit resistance then GI earthing plate or rod. Lets clear this fundamental regarding as often falling in this trap will lead to higher investment on earthing by using copper as earthing material. If one considers a plate electrode, the approximate resistance to earth is: Resistance formula for Pipe earthing (R) = (100r/2πL) X loge (4L/d) ·           L= Length of Pipe/Rod in cm d=Diameter of Pipe/Rod in cm r = Resistivity of Soil Ohm-meter. Resistance formula for Plate earthing (R) = (r/A) X   under root(π/A). ·          r = Resistivity of Soil Ohm-meter. ·          A=Area of Earthing Plate m3. As can be seen ...

Difference Between Grounding and Earthing: Myths vs Standards Electrical safety often raises confusion between the terms grounding and earthing . Many people assume that grounding refers only to the connection of current-carrying conductors (like transformer or generator neutral) to earth, whereas earthing refers to the connection of non-current carrying metallic parts (like enclosures, motor frames, or panels). 👉 This distinction is actually a myth. According to recognized standards, both grounding and earthing mean the same thing . The confusion mainly arises from differences in terminology across countries. Grounding vs Earthing: Origin of the Terminology British English (UK, IEC, IS): Uses the word Earthing . American English (USA, IEEE, ANSI): Uses the word Grounding . So, it’s more a matter of language preference than technical difference. Standards and Definitions IS 3043:1987 (Code of Practice for Earthing) The term...

Misconceptions About Fault Current Direction in Electrical Systems In electrical engineering, there are widespread misconceptions regarding the direction of fault current . Many assume fault current simply flows from the source to the load , as in normal operation. However, this interpretation is misleading and can cause incorrect system protection design. Fault Current Flow – The Correct Understanding Under normal conditions, current flows from source → load . During a fault at the load end , the effective resistance/impedance at the fault point reduces drastically (almost to zero) . As a result, the fault current appears to “flow backwards”: the load-end protection sees the fault first and should trip before the transformer or upstream breaker. In reality, although current is still drawn from the source, the magnitude and point of detection of fault current is determined by the fault location . 👉 That is why modern electrical systems are designed to ensure prote...

Star Delta Starter connected motor direction can be changed by changing either connections at main input line connections and O/P connections at Main and Delta contactors. Star-Delta Starter Connection changing circuit is shown above.

Why Induction Motors Are Not Kept Running in Star Connection Induction motors are sometimes started in Star connection (using a Star-Delta starter) but are always run in Delta for normal operation. The reasons are: 1. Voltage Reduction in Star In Star connection, V p h a s e = V l i n e 3 V_{phase} = \frac{V_{line}}{\sqrt{3}} This means each winding receives only 57.7% of the line voltage . 2. Current Reduction Since I p h a s e = I l i n e I_{phase} = I_{line} , the line current drawn is lower. Current is reduced in proportion to the reduced voltage. 3. Torque Reduction Motor torque is proportional to the square of the applied voltage : T ∝ V 2 T \propto V^2 So, in Star: T s t a r = ( 1 3 ) 2 × T d e l t a = 1 3 T d e l t a T_{star} = \left(\frac{1}{\sqrt{3}}\right)^2 \times T_{delta} = \frac{1}{3} T_{delta} This means the motor can produce only one-third of the rated torque . 4. Power Reduction Motor input power is proportional to voltage × ...

Star-Delta Starter: Working Principle, Circuit, and Applications Introduction For induction motors up to 7.5 kW , a Direct-On-Line (DOL) starter is commonly used. However, for motors above 7.5 kW , starting them directly causes large inrush currents that can disturb the supply voltage. To overcome this, industries widely use the Star-Delta Starter —a simple, reliable, and economical motor starting method. Working Principle of Star-Delta Starter The Star-Delta Starter reduces the motor’s starting current by initially connecting the stator windings in Star (Y) and later switching to Delta (Δ) after a preset time. 1. Star Connection (Wye) Phase current = Line current Phase voltage = Line voltage ÷ √3 Starting voltage reduced by 1/√3 (≈58%) Torque reduced to 1/3 , since torque ∝ V² Starting current reduced to 1/√3 of DOL current ✅ Advantage: Reduced inrush current. ❌ Limitation: Reduced starting torque. 2. Delta Connection (Δ) Phase voltage = Line voltag...